Riociguat can be used to treat chronic thromboembolic pulmonary hypertension (CTEPH) or pulmonary hypertension, which has a structural formula as follows:

Chem. Med. Chem. 2009, 4, 853-865 reports the following method:

1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridine-3-formamidine hydrochloride is an important intermediate for synthesis of Riociguat.
In respect to the preparation of 1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridine-3-formamidine (hereinafter referred to as “compound 8”) hydrochloride (hereinafter referred to as “compound 11”), US20020173514 reports the following method:

Reagents and yield of the reaction in each step: (I) trifluoroacetic acid (TFA), 1,4-dioxane; (II) 3-dimethylaminoacrolein, TFA, two steps 49.9%; (III) ammonia (NH3), methanol, 100%; (IV) trifluoroacetic anhydride, pyridine, tetrahydrofuran (THF), 100%; (V) sodium methoxide, methanol (MeOH), 100%; (VI) ammonium chloride, acetic acid (CH3COOH), methanol, 76.4%.
This reported synthesis method has the following defects: raw material (1) and raw material (2) are hardly available in domestic market and are expensive; the yield in the first two steps is low; the postprocessing of (II) needs column chromatography; mass production cannot be realized.